In reprocessing nuclear fuels the "feed clarification" step of the method produces a feed sludge in the form of a suspension which must be further treated and conveyed to final storage. For doing this, two different methods are used at present. The one method involves so-called "cementation", i.e., the bonding of the sludge suspension into cement mortar. The other method involves "vitrification". By both methods, solid bonds are generated, capable of final storage in which the feed sludge is fixed.
Feed clarification is usually effected by means of a centrifuge or by means of filters. The feed sludge suspension is discharged into a feed sludge container arranged directly below the centrifuge. From this container, the feed sludge suspension must be conveyed through pipes to the vitrification device. Independently of the further treatment of the feed sludge, glass frit is fed to the vitrification device. The conveyance of the feed sludge suspension is effected hydraulically by the sludge being sucked out of the feed sludge container by means of a steam-driven ejector nozzle and conveyed together with the condensate from the driving steam to the vitrification device. In this process, the sludge suspension leaving the centrifuge at high solids concentration becomes diluted by the condensate, which necessitates separating the suspension being conveyed from excess water of conveyance. Furthermore, the selection and design of the ejector conveyor section of the apparatus requires great care in order to guarantee blockage-free conveyance of the sludge to the next step of the process. In addition, the length of a hydraulically operated conveyor line is limited. This is disadvantageous because conveyance to the "vitrification" step of the method requires traversing a distance of over a hundred meters. By interposition of a further steam ejector, greater distances may indeed be traversed, but this increases the dilution of the sludge suspension which in turn increases the expense of separating the excess water from the sludge.